OBJECTIVE--To assess and compare the roles of transthoracic and transoesophageal echocardiography in the diagnosis and management of an aortic root abscess. DESIGN--To select patients with echocardiographic diagnosis of aortic valve endocarditis with and without an aortic root abscess and correlate this with a retrospective review of surgical and necropsy data. SETTING--Tertiary referral centre at a university teaching hospital. PATIENTS AND METHODS--34 patients with confirmed aortic valve endocarditis were treated over a four and a half year period. All patients underwent both transthoracic and transoesophageal echocardiography with 17 patients having biplane or multiplane imaging. RESULT--11 patients (32%) had an aortic root abscess. Transthoracic echocardiography identified four cases of aortic root abscess whereas transoesophageal echocardiography correctly detected all 11 cases and also detected complications including mitral aortic intervalvar fibrosa fistula in two patients and right atrial involvement in another two patients. Only biplane imaging was able to show an anterior aortic root abscess in one patient and the circumferential involvement of the aortic annulus in another two patients. All patients with an aortic root abscess were treated surgically after transoesophageal echocardiographic diagnosis. After operation, prosthetic aortic regurgitation was present in seven patients and a repeat operation was performed in three patients. Only transoesophageal echocardiography detected a postoperative aorto-right atrial fistula in two patients and recurrence of the root abscess in another. There were five deaths in hospital (45%). CONCLUSIONS--Compared with transthoracic echocardiography, transoesophageal echocardiography was more sensitive and more specific for the early diagnosis of aortic root abscess and its complications and facilitated both the preoperative and postoperative management of these patients. Biplane and multiplane imaging provide additional diagnostic information. All patients with suspected aortic valve endocarditis should have an early transoesophageal echocardiographic study.